Undersea

Niue is a very small island of about 250 square kilometre lying North-East of New Zealand, 10 degrees past the date meridian and 19 degrees south of the Equator (170ºW, 19ºS). One can fit Niue in Lake Taupo twice, with room to spare, as it is oval shaped about 20 by 15 km. On the way to Niue by sea (2400km), one would pass the Kermadec Islands (800-1000km) which form NZ’s northernmost outcrop. In May 2002 I visited these islands and made some ecological discoveries that, when correct, should apply equally to Niue, another isolated island amidst an ocean desert. The map shows Niue amongst Pacific island groups, and its Exclusive Economic Zone (EEZ) of 390,000km2 in yellow. Apart from a desire to dive in clear warm water, Niue attracted me because of its (presumed) simple ecology and resemblance to the Kermadec Islands. We had to postpone our trip planned for September 2003, and then came Cyclone Heta (January 2004), which should have extinguished my desire since it destroyed so much of Niue both above and under water. This however, made the visit even more attractive for me, because where on Earth could one study the (natural) degradation by the largest cyclone ever measured on an island that does not have any unnatural degradation from runoff, sewage or industrial pollution (but some from fishing)?

Niue suited me to a tee, because where could one find a remote tropical island with incredibly friendly and civilised people, educated the New Zealand way and all speaking English? It is a place where you won’t need to lock your car because it is entirely safe. No traffic lights, traffic pile-ups, Warrants Of Fitness, OSH, speed traps and drunk-driving blitzes. It’s a place where everyone greets everyone else (and perhaps also knows everyone else), where police and customs make jokes and smile, where nobody hassles you for your money, where you can go about your business in your own way, where you don’t find DO NOT signs, no speed limits (but everyone drives 50-60km/h) and other niceties of our civilisation which we deem so necessary.

But it is also a poor country, with precious few resources, a top heavy government bureaucracy and lots of aid money that does not want to cling to this island. It suffers from hemorrhaging its own people to Auckland where 20,000 live as only 1100 remain on the island. Translate this to mean that living on Niue has tremendous disadvantages. Many houses (4 out of 5?) stand empty and derelict as mementos of more populated times.

But for the tourist it means warm but not hot days, with an annual average temperature of 24.7ºC, a cool breeze during the day and balmy evenings. The water is pleasant but not warm, between 25 and 27ºC (although this has never been measured over time). You need a wet suit for diving, but you can swim pleasantly for an hour or more in winter (but watch that sun burn). Saturdays and Sundays the island appears deserted as people have traditional things to do. The Saturday is for working the land or for communal working-bees while the Sunday is strictly obeyed for rest, and people go to church twice or more. Boats are not allowed to go out and there is no diving or fishing.

Diving in Niue is an experience because of its very clear water with visibility between 30 and 60m, and usually 50m. It gives new meaning to snorkelling when, from the surface, details can be identified at 30m deep. The environment is as expected poor in both biodiversity and fish densities but that is made good by extensive caves in shallow water and a community of survivors, each having some special adaptation in order to survive in these austere and exposed conditions. That is what this story is about – diving with the survivors.

A diver hangs motionless between surface an bottom, experiencing the extreme clarity of the water.

Snorkelling is a new experience, being able to distinguish a sea cucumber at 30m depth. This photo was taken with a normal 28mm lens to avoid distortion.

A diver enters one of many caves honeycombing the coralline flats surrounding the island.

A typical dive scene near the Matavai Resort, where most corals have been spared Heta’s wrath.

An Acropora plate coral reaches for the sky, having suffered two chips from last storm.

Where the cyclone struck
Niue is oval shaped and located at the southern end of cyclone paths, its north-western side struck by cyclones, whereas its south-eastern side continually buffeted by deep swell powered by a moderate but constant breeze of 10-20 knot, the trade winds. These do not blow all year round and come to a calm in summer (Jan-Apr).

The map shows how Niue has two distinctly different sides, one buffeted by mild trade winds, the other sheltered most of the time, but occasionally struck by the worst a cyclone can offer. Heta struck in January 2004, Ofa in 1990 and one before that in 1979. The map also shows estimated damage from Heta by the width of the red contour. Due to the shape of the sea bottom at Alofi and because its coast faced the storm head-on, most of the damage occurred here. Going north, the coast veers off the storm, but then again facing the full brunt between Makefu and Uluvehi. But because the coast runs steeper without a platform, waves must have bounced their energy back to sea rather than dissipating it on the shore. Some damage was caused between Tepa point and Avatele, but most of the damage there originated from earlier cyclones.

Cyclones are just large storms which have the habit of laying bare an underwater zone or barren. In New Zealand such storms remove seaweeds, causing barrens, which are then maintained and widened by grazers of which the sea urchin and Cooks turban shell are the most voracious. Likewise, regular cyclones cause barrens, roughly corresponding to the red zone on the map. After removal of proud corals, the barrens in Niue really look bare, but on closer inspection, produce a rich supply of fast growing algae. Corals do not easily re-conquer these barrens because of the many biting teeth here and because corals grow rather slow in this cool tropical sea with very little nourishment. Not surprisingly, most of the marine organisms here are grazers, from snails to sea urchins to grazing fish. They truly benefit from cyclones and they are the true survivors. But grazing alone is not a sufficient recipe for survival.

The exposed side of a coral bommy shows up to 50% live coral cover but also a large proportion of coral-building algae. Near Avatele.

The exposed side of same coral bommy shows only about 5% live coral. It is a barren, still growing in size due to the coralline algae that survive storms better.

On closer inspection, the barrens are very productive, supporting armies of grazers like these nocturnal snails, nocturnal sea urchins and daytime fish.
The large scrape marks are from parrot fishes; the thinner ones from surgeon fishes and the crisscross marks from sea urchins.

Seaweeds survive the chaos by ‘turfing’, growing old and reproducing asexually by means of runners. In this picture a green seaweed and several red seaweeds colonise the area by turfing it over with runners. Many cover themselves in coral sand as a protection against sand-blasting and over-enthusiastic grazers.

This nocturnal sea urchin has a strong homing instinct, enabling it to venture far from its daytime hideout. This homing knowledge is critical to its survival.

This robust grazing snail has a very small opening to protect it from crab attacks. Through the gap it extends a wide and strong foot, enabling it to graze on wave-swept platforms and to weather large storms.

Niue has a surprisingly large number of sea urchin species, nearly all well hidden during the day. This bar-spined Diadema species folds its long spines into a cylinder as it hides away in a narrow slit or tunnel. (Diadema setosum)

This beautiful large soft-shelled shore crab has long and strong legs, enabling it to scoot over the coral flats and through rock pools. It can also stay out of the water for some time to weather storms. It feeds mainly on algae. (Grapsus grapsus tenuicrustatus)

By burrowing into the limestone coral rock, these needle urchins are protected against the worst conditions. They are usually found where indeed the environment is pummelled with loose debris.

Most of the fish in Niue are grazers, swarming the reefs like these surgeonfishes, grazing the shallow platforms during high tide and visiting rock pools. Here is a school of speckled surgeonfish (Acanthurus guttatus)

The marine environment
With barren zones extending to over 30m deep off Alofi, what would the other side look like? In September the trade winds are well established and diving there amounts to suicide. But between Tepa Pt (pronounce: sepa) and Limufuafua Pt at the island’s very southern end, the coast curves away from the tradewind tumult, offering a chance for a dive. This dive should show us what the protected wild coast looks like under water, and thus what the marine environment looks like without regular destruction from cyclones.

It became a memorable dive with minimal gear to reduce friction, only a pony tank and no buoyancy compensator. All the same, the swell moved me over distances of 7-15m across a razor sharp reef, ready to shred suit and skin. The only way to take photos was to time the position of the shot with the return of the water’s swing, quickly planting the tripod and taking a photo. I didn’t expect them to look any good, but the 13mm fish eye lens was quite forgiving.

It’s a calm day and the sea does not show white caps. Yet the swell, animated by long periods of winds blowing from one direction, breaks and spills over the coral flats, making diving here impossible.

The marine environment of the wild side is rich in corals and desirable seafood like this large Tridacna giant clam (Tridacna maxima), showing its outside folds undamaged by storms. Yet even here one finds many barren patches formed by coralline algae, an important reef builder, if not THE most important reef builder.

From this relatively pristine environment to one of the favourite dive spots near the Matavai Resort, shows the gradual procession to the barrens at Alofi.

The corals near the Matavai Resort show variety and damage, recent and from storms long past. It shows broken corals amongst the living, and in rubble fields.

Down from 25m depth, the plate corals look untarnished as they dominate space, being able to grow much deeper still, due to the very clear water. It is here where the barrens stop and the deep reef begins. (Acropora hyacinthus)

Acropora corals grow relatively fast like this kind of stagshorn coral. They survive by being hard and strong, yet growing relatively fast, designed to dominate space first. On right two Acropora plate corals.

one of the survival strategies of some corals is not being brittle but leathery, like this coral with long polyps resembling an anemone. (Sarcophyton elegans)

The Alofi scene is that of extensive rubble fields and barren rocks, with coral-grown ridges descending from 15m to 30m. These suffered most damage because they are located out of reach of debris and damage by normal storms. The lesson is that large storms nibble away at the edges untouched by lesser storms, causing large damage to those corals that managed to grow there inbetween. Such large storms widen the grazed barrens, which may or may not be repopulated with corals, depending on the voracity of existing grazers and how these survived the storm.

One of the survival strategies of some corals is not being brittle but leathery, like this coral with long polyps resembling an anemone. (Sarcophyton elegans)

Barren and broken rock and bent steel beams are now but mementos of the storm’s brute force.

The survivors and their strategies
We were lucky to photograph many of Niue’s common animals, being able to show how each has a strategy for survival. By means of photographs we like to tell their stories here.

The sea snake is an active hunter by day but sleeps by night. It lives happily on land in case of averse conditions in the sea. These poisonous snakes have intimate knowledge of their ranges, knowing where to leave the sea inside underwater caves, where they also lay their large eggs. This sea snake is sleeping in a protective cavity in the coral rock.

A very effective survival strategy is to leave the water. These land crabs live on land for most of their lives, but return their eggs to the sea to complete their life cycles. This large crab was encountered by night on the coral-sealed road. It uses one leg like a blind man’s cane. (Discoplax longipes)

This most amazing rock skipping blenny leaves the water for long times in the day, being able to move fast over the rocks and over the water’s surface. It shelters in small cracks and hollows in the shallows.

The banded coral shrimp (Stenopus hispidus) surprised us most because it survived inside rockpools and shallow water, even though being so fragile. It shows just how much shelter can be found inside coral cavities. Being a cleaner shrimp, fish bring its food towards it, so it does not need to expose itself in search of food.

This large armoured pineapple sea cucumber survived by being armoured on its back and having thousands of strong tube feet to hold itself in place. It too has a good knowledge of where it lives. (Thelenota ananas)

The armour plates of the pineapple sea cucumber resemble the scales of a pineapple. This sea cucumber feels hard and sharp to the touch. Its strategy is to find a sheltered spot, suck on hard to bare rock, and survive being pummelled by debris.

f043928 (left) and f043929 above: the slipper coral is a wandering ‘mushroom’ coral which does not attach itself to the coral rock. It is claimed that it can support itself on the tentacles extending from its hollow foot. By night it shows long polyps. Its strategy is to be moved by waves, such that it always lies on top of other corals, and cannot easily be outgrown by them. (Herpolitha sp)

Just before sunset there were no feather stars on the reefs, yet before we began our night dive, they were all there, occupying strategic commanding views. Their survival strategy is their homing instinct and being able to walk distances of 2-10m.

Just before sunset there were no feather stars on the reefs, yet before we began our night dive, they were all there, occupying strategic commanding views. Their survival strategy is their homing instinct and being able to walk distances of 2-10m.

These colourful and dainty christmas tree fanworms live inside tubes encapsulated by growing Porites coral. They can withdraw inside their tubes, closing the hatch with the caps shown here. (Spirobranchus giganteus)

This strange snail lives its entire life in a horn cemented inside a Porites coral. It can filter plankton or throw a sticky catch net as shown here, to catch food. Later it will pull the net in and gobble it up, including any caught food.

Survival does not only depend on weathering the worst of storms, but also on being bale to live in the barren habitats made by these storms. Not surprisingly, most fish are grazers. A most notable and colourful group consists of surgeon fishes or tangs, named after the tang, a sharp spike or scalpel that these fish carry on their tail stocks. It makes them almost invulnerable to predator attacks, and this in turn enables them to grow old, which is necessary for surviving on a small island surrounded by a desert sea.

The convict tang (Acanthurus triostegus) scours the shallows in groups, but by night sleeps on its own where it slowly discolours, showing patches on its sides.

The speckled tang (Acanthurus guttatus) schools by day but sleeps individually by night. It does not change colour remarkably.

The velvet tang (Acanthurus nigricans) is a very beautiful fish, here seen before bedding down. It is common in Niue.

The Achilles tang (Acanthurus achilles) is conspicuous by its orange spot and fine white lines.

Large fish like this beautiful parrotfish asleep at night, can swim to deeper and sheltered water during storms. Their main threat is being fished and eaten, but parrotfishes have earned some immunity by being poisonous at times, infected by ciguatera.

An unidentified butterfly fish, common in Niue, is one of the surprises. What secrets is it hiding?

Niue seems like Noah’s ark at times, having a little of many different species. The black spotted puffer (Arothron nigropunctatus) is common and easy to photograph at night.

storms rounded the shape of this large spider shell which has lost its outer cusps, but inside, the snail is thriving and surviving. These shells also grow old, particularly in an environment deprived of food.

this harmonica sea cucumber visits a large area without even leaving home, as it is able to inflate itself from an insignificant blob to over one metre in length. Homing then becomes easy. (Opheodesoma australiensis)

Large areas are mysteriously covered in ‘loose’ sand which proves not to be loose at all but held firmly by turfing algae underneath. Here the sand has been removed with some difficulty to expose the algal mat. The cover of sand protects against being sand-blasted.

Three large sea cucumbers in a small rock pool have protected themselves with sand against being sand blasted.

Summary

Diving in Niue is an unforgettable experience because of its ultra clear warm waters. But clear waters are also poor in nutrients, resulting in low densities of fish, while corals grow slowly for the same reason. Niue has an additional disadvantage that it is a single, small island surrounded by a large empty ocean. Because the larvae of most species spend some time near the water’s surface before descending onto a reef, most of them float away into an ocean devoid of food, and no place to settle. The chance of them ‘recruiting’ on the island is indeed very small. The ocean currents around Niue are driven by south-Easterly trade winds originating from even poorer and clearer seas that are also cooler. Thus Niue is showered with very few new arrivals from elsewhere. As a result, the species found in Niue must depend on their survival skills in order to thrive in sustainable populations.

growing old

because reproduction has a low chance of success, age should make up for this, as it creates more opportunity for a successful recruitment.

nest care

rather than spawning in open water, small fish benefit from caring for their eggs until these hatch. Many such nests are made in the protective shelter of rock pools where plankton productivity is higher due to higher temperatures, reflected light from coralline flats and nutrients percolating from the land. The water inside rock pools is also less likely to flow away on ocean currents, which enhances the chance of recruitment (settlement).

turfing roots

because the water is comparatively cooler than in the warm tropics, and because of the regular damage from cyclones, turfing algae are the primary survivors. They multiply asexually by means of running roots, so their pelagic spores are not of critical importance. Most of the reefs are constructed by coralline algae, known as ‘pink paint’ that thrives better than the corals. The pink paint encourages the growth of fine algae that are easily removed by many grazers, from snails to sea urchins, to grazing fish.

living from algae

since the main food around Niue is produced by short algae, all species adapted to eating plant food, survive better and in higher numbers. Even omnivores such as the local green crayfish, thrives on algae.

hiding and homing

the ability to hide and to home back to one’s hiding spot, is of critical importance to survival. Any night dive shows just how many animals exhibit this behaviour, from grazing snails and cowries to sea urchins and grazing fish.

leaving the water

leaving the water during averse conditions is a good strategy available only to few animals. Sea snakes probably do this.

burrowing and living in tubes

the coral rock is relatively easy to dig into because it can be dissolved by acids. Sea urchins are particularly successful at this. Others cement their tubes to growing corals, using the coral as protection. These include snails, fan worms and crustaceans.

being robust

some organisms can grow old while surviving the direct impact from flying rubble. These include an awesome large armoured sea cucumber and large snails such as Tridacna and spider cowries.

swelling and shrinking

an age-old protection mechanism is that of swelling when times are right and shrinking when they ae not. Anemones, soft corals, tube corals and some sea cucumbers use this method to protect themselves.

covering with sand

if one is not able to burrow, a cover of sand suffices as protection against sand blasting or being rough-handled by turbulent water. We’ve seen it used by algae and sea cucumbers. Small gobies living in small sand pools inbetween larger rocks, also survive well.